The mechanical interplay between cell and the surrounding microenvironment is largely recognized to critically regulate cell function in tumor progression, malignancy transformation and metastasis but it remains poorly understood due to the lack of suitable measurement tools. While much progress has been achieved in the context of single-cell measurements of forces and deformation, measuring intracellular and extracellular moduli remains challenging, especially in 3D microenvironments. Yet, cell/ECM mechanical properties are known to be important because they link the presentation of an environmental mechanical stimulus to the activation of a mechano-related signaling pathway. In the past few years, we have been developing an all-optical approach to this challenge, named Brillouin microscopy. Brillouin cellular microscopy promises to map the intracellular and extracellular elastic modulus at high resolution, non-perturbatively, without contact in 3D microenvironments. As shown in strong preliminary data, we have achieved several key milestones that demonstrate our ability to measure relevant mechanical properties at a cellular and sub-cellular level. In this research we will develop and validate our microscopy platform for cancer-related studies. Aim 1 will focus on the advanced development of the instrument to reach rapid mechanical imaging at sensitivities comparable to contact-based mechanical tests. Aim 2 will focus on a direct validation of our technology against gold-standard techniques using properties and settings known to be relevant for metastatic progression. Finally, Aim 3 will test our technology within the context of tumor cell extravasation, a challenging experimental setting where no other technology can perform mechanical characterizations. Achieving sufficient speed and sensitivity for extravasation will guarantee the broad applicability of our technology for tumor mechanobiology and vividly demonstrate the type of novel information that our technology can provide. Importantly, Brillouin technology will be integrated into confocal microscopes to add a mechanical modality to widely-used instruments. The rigorous process of technology development, validation, benchmarking and field-testing will yield an instrumental platform with unprecedented capabilities to study cell-matrix biomechanics and ready to be widely adopted by the cancer biology research community.